In 1975, Allentown, Pennsylvania and Youngstown, Ohio could be considered of a piece. Both were mid-sized cities in which nearly 35% of the local work force was employed in manufacturing. By 1983, both had taken on the moniker of the "rust belt"; dual processes of deindustrialization and hollowing out pointed toward bleak futures. Yet, twenty years later, it is clear that the cities' economies have actually proceeded down dramatically divergent paths. Allentown has found itself on the high-road of economic change (Harrison and Bluestone 1983; Piore and Sabel 1984; Kochan, Katz and McKersie 1986; Dertouzos, Lester and Solow 1989) while Youngstown has fallen into a lean and mean race to the bottom (Applebaum and Batt 1994; Harrison 1996). Challenging both learning region (Amin and Thrift 1994; Florida 1995) and communitarian social capital (Putnam 2000) perspectives on sub-national socio-economic change processes, this thesis argues that the cities' economic divergence can be traced to differences in the social structures in which firms are embedded (Romo and Schwartz 1995). Social embeddedness perspectives reject explanations based on either broad categorizations or pure efficiency in favor of ones that take into account the concrete structure of actors social networks (Granovetter 1985; DiMaggio and Powell 1990). These networks shape action both by determining access and control over information and resources as well as by defining the contexts in which actors' world views are rooted (Padgett and Ansell 1993; Podolny 1998). The research presented in this thesis is unique in that it combines sub-national historical comparison (c.f., Locke 1995; Saxenian 1996; Molotch, Greidenberg and Paulsen 2000) with longitudinal data on the structure of board(cont.) interlocks (c.f., Galaskiewicz 1985; Romo and Schwartz 1995) to show how the specific structure of social networks within communities constrains and enables social action in the face of externally generated crises. Thus, it takes up the challenge to use network analysis to "pinpoint [the] causal mechanisms whose combinations produce the actual histories we observe" (Tilly 1992; Emirbayer and Goodwin 1994). Despite sharing remarkably similar economic histories, the social structures of Allentown and Youngstown developed along two very different trajectories. In Youngstown, a dense core of elites emerged in the 19th century which kept tight control over local industry which was centered on steel production. In Allentown, two groups of elites emerged early on that were associated with two separate industrial groups (also centered on steel). These groups competed with each other throughout the first century of the region's economic growth. The difference had important consequences early in the 20th century as industrialization gave way to Eastern European immigration and industrial union organizing activity in the 1930s. In Youngstown, social divisions within the community were essentially class-oriented leading to violent clashes as the core elite "circled the wagons" in the face of ethnic and later labor conflict. In Allentown, the most salient divides were based on communities within the region and their associated industrial blocks. Social conflict was less contentious as actors drew on cross-class social networks to find common ground. These differences were vitally important in the 1950s when the cities started ...